This invention relates to improvements in systems for handling and conveying packages, and, more particularly, to a conveyor system having a belt which moves along a combination roller-slider bed surface and which is powered through a shaft-mounted gear drive positioned outside of the conveyor system frame, with means for controlling acceleration and deceleration of the belt.
Systems for handling and conveying packages are known and generally have comprised a slider bed conveyor having a wide endless belt which slides over a solid smooth surface usually made of steel. Such systems are usually powered by an assembly of drive pulleys on which the belt is mounted which in turn are driven by a motor, gearbox and chains or other power transmission components which are mounted below the conveyor belt and within the frame of the conveyor, all of which caused the prior art design to be higher, wider, longer and more difficult to work on. Such prior package handling and conveying systems have performed satisfactorily in situations involving relatively light loads and work cycles not involving frequent starting and stopping. However, recent attempts to adapt such slider bed conveyor systems to new industries has exposed inherent weaknesses and inefficiencies in such systems and has not been entirely successful.
In recent years, the overnight package delivery industry has grown to the point where there is a relatively short period of time to collect, sort and deliver hundreds of thousands of packages in order to meet the promised delivery deadlines. The main requirements of conveyor systems used in the package delivery industry are the ability to run reliably with minimal preventive maintenance and the capacity to handle heavy loads with frequent starting and stopping, all in a system located within a minimum of space. Attempts to adapt the prior art slider bed conveyor systems to the overnight package delivery industry have not been entirely satisfactory. The placing of numerous packages on the conveyor belt creates a heavy load which causes high friction forces between the belt and the slider bed, thereby causing excessive heat build-up which has no method of escaping. This excessive friction heat build-up causes several mechanical and operating problems such as causing the conveyor belt backing material to disintegrate and become gummy whereby it adheres to the slider bed surface and the belt drive pulleys, further increasing friction in the system and causing even faster deterioration of the belt, and wear on the other components. The heat build-up also causes lagging on the belt drive pulleys to delaminate causing premature failure and downtime of the system for repair. The above conditions lead to belt slippage, thus accelerating the heat build-up and the other described problems. Finally, the excessive heat build-up can cause damage to heat sensitive products handled by the system. The excessive friction of the belt causes increased belt tension which in turn causes additional mechanical and operating problems in the form of reduced belt life and reliability; reduced life of the belt lacing; less efficient operation resulting in higher operating costs for energy and replacement of failed components (e.g. chains, sprockets, bearings, motors or gear reducers.)
Prior to this invention, the solution to the problems mentioned above has been to use larger components having more capacity and horsepower to overcome the increasing loads, forces and inefficiencies of the system. The larger components and structures necessitated larger motors, gearboxes and chains, or other transmission components, to accommodate the forces and energy requirements involved. Even with the increased size and power of the modified systems, the increasing loads placed on the conveyor belt caused the friction problem to remain and caused an additional problem to be placed on the belt during starting and stopping of the system. The prior art systems had no means for regulating the acceleration of the drive system to lessen the jerking of the load during start up, causing premature failure of the belt and belt lacing means. As drive sizes were increased to overcome problems caused by friction, the forces caused during acceleration exacerbated all the previously described component wear and failure. All of these factors combined to cause high maintenance costs, high energy usage because of the system inefficiencies, and generally an unreliable conveying system in an industry requiring high reliability.